为什么通过 IndexOf() 找不到 CheckedListBox 中存在的项目？

Question

我有这个代码：

if (currentWeekSaved)
{
    DateTime currentWeek = Convert.ToDateTime(comboBoxWeekToSchedule.SelectedValue);
    AssignmentHistory ah = AYttFMConstsAndUtils.AssignmentHistList
        .FirstOrDefault(i => i.WeekOfAssignment == currentWeek && i.TalkType == BIBLE_READING_TALK_TYPE);
    if (ah != null)
    {
        var assignedStudentFirstname = AYttFMConstsAndUtils.GetStudentFirstNameForID(ah.StudentID_FK);
        var assignedStudentLastname = AYttFMConstsAndUtils.GetStudentLastNameForID(ah.StudentID_FK);
        assignedStudent = new Student() {FirstName = assignedStudentFirstname, LastName = assignedStudentLastname, StudentID = ah.StudentID_FK};
    }
}
List<Student> BRStudents =
    AYttFMConstsAndUtils.StudentsList.Where(h => h.EnrolledInAYttFM)
        .Where(i => i.RecommendedNextTalkTypeID.Equals(BIBLE_READING_TALK_TYPE))
        .OrderBy(j => j.WeekOfLastAssignment)
        .ToList();
if (null != assignedStudent)
{
    // If exists in list, remove it first, and then add it back at the top
    //int assignedStudentIndex = BRStudents.IndexOf(assignedStudent);
    int assignedStudentIndex = checkedListBoxBR.Items.IndexOf(assignedStudent.FullName);
    if (assignedStudentIndex > -1)
    {
        BRStudents.RemoveAt(assignedStudentIndex);
    }
    BRStudents.Insert(0, assignedStudent);
}
checkedListBoxBR.DataSource = BRStudents;
checkedListBoxBR.DisplayMember = "FullName";
checkedListBoxBR.ValueMember = "StudentID";

如果已经有人为正在处理的那一周分配了人，我想先将他们从 checkedListBoxBR 中删除，然后再将他们添加回索引 0。但是，即使这个人是在 checkedListBoxBR 中，这一行：

int assignedStudentIndex = 
    checkedListBoxBR.Items.IndexOf(assignedStudent.FullName);

...找不到它们。 "assignedStudent.FullName" 的值确实等于其中一项的值；如上所示，"FullName" 是 CheckedListBox 的 ValueMember:

通过它，学生列表 BRStudents 有 2 个成员，一个已经分配的人和另一个人； "assignedStudent"是已经分配的人； checkedListBoxBR 有三个项目，已分配的人加上两个其他人。

那么，当分配的人用 FullName 表示时，为什么 assignedStudentIndex -1？确实，我没有在这一行中明确分配 FullName：

assignedStudent = new Student() {FirstName = assignedStudentFirstname, LastName = assignedStudentLastname, StudentID = ah.StudentID_FK};

...但是 FullName 是 class 中的一个计算字段：

public class Student
{
    public int StudentID { get; set; }
    . . .
    public string FirstName { get; set; }
    public string LastName { get; set; }
    . . .
    public string FullName
    {
        get
        {
            return $"{FirstName} {LastName}";
        }
        set { } 
    }
}

那么，为什么在 CheckedListBox 的项目中找不到 "So and So" 最明确的地方？

更新

Olivier 的建议似乎不错 ("iterate through checkedListBoxBR.Items and see if you find a match between the item's DisplayMember and the assignedStudent.FullName")。但是怎么办？我想也许像这样的东西可以做到：

for (int i = 0; i < checkedListBoxBR.Items.Count; i++)
{
    if checkedListBoxBR.Items[0].DisplayMember.Equals(assignedStudent.FullName)
    {
        checkedListBoxBR.RemoveAt(i);
    }
}

...但是 "DisplayMember" 在这里不被识别（"RemoveAt" 也不被识别）。

更新 2

响应 Olivier 的建议，我将以上内容修改为：

for (int i = 0; i < checkedListBoxBR.Items.Count; i++)
{
    if checkedListBoxBR.Items[i].DisplayMember.Equals(assignedStudent.FullName)
    {
        checkedListBoxBR.Items.RemoveAt(i);
    }
}

...但它仍然认为 DisplayMember 属性-不受欢迎。

更新 3

我已经简化了代码，并且运行良好。这是简化版：

// Called whenever the week changes (a new week is navigated to/selected in the combobox)
private void PopulateBibleReadingComboBox()
{
    int BIBLE_READING_TALK_TYPE = 1;
    Student assignedStudent = null;
    List<Student> assignedStudents = null;

    // If the week has been saved, get the student who has been assigned the Bible Reading
    if (currentWeekSaved)
    {
        DateTime currentWeek = Convert.ToDateTime(comboBoxWeekToSchedule.SelectedValue);
        AssignmentHistory ah = AYttFMConstsAndUtils.AssignmentHistList
            .FirstOrDefault(i => i.WeekOfAssignment == currentWeek && i.TalkType == BIBLE_READING_TALK_TYPE);
        if (ah != null)
        {
            var assignedStudentFirstname = AYttFMConstsAndUtils.GetStudentFirstNameForID(ah.StudentID_FK);
            var assignedStudentLastname = AYttFMConstsAndUtils.GetStudentLastNameForID(ah.StudentID_FK);
            assignedStudent = new Student() {FirstName = assignedStudentFirstname, LastName = assignedStudentLastname, StudentID = ah.StudentID_FK};
            // Use the ID to get the student and put him/her in a 1-person list (needed for
            // the subsequent LINQ Union)
            assignedStudents =
                AYttFMConstsAndUtils.StudentsList.Where(i => i.StudentID == ah.StudentID_FK).ToList();
        }
    }
    // Get all the candidates for assignment
    List<Student> BRStudents =
    AYttFMConstsAndUtils.StudentsList.Where(h => h.EnrolledInAYttFM)
        .Where(i => i.RecommendedNextTalkTypeID.Equals(BIBLE_READING_TALK_TYPE))
        .OrderBy(j => j.WeekOfLastAssignment)
        .ToList();
    if (null != assignedStudent) 
    {
        List<Student> allBRStudents = assignedStudents.Union(BRStudents).ToList();
        checkedListBoxBR.DataSource = allBRStudents;
        checkedListBoxBR.DisplayMember = "FullName";
        checkedListBoxBR.ValueMember = "StudentID";
    }
    else // No assigned student found, bind to the candidate students only
    {
        checkedListBoxBR.DataSource = BRStudents;
        checkedListBoxBR.DisplayMember = "FullName";
        checkedListBoxBR.ValueMember = "StudentID";
    }
    // In either case, highlight and check the first one now
    checkedListBoxBR.SelectedIndex = 0;
    checkedListBoxBR.SetItemChecked(0, true);
}

Answer 1

我可以看出两点错误。

首先，您填充 checkedListBoxBR ，然后 检查是否存在某个项目。

其次，你在比较苹果和橘子。 checkedListBoxBR.Items 是对象的集合，您正在通过 indexOf 将其与字符串 (assignedStudent.FullName) 进行比较。那是行不通的。

更好的解决方案是遍历 checkedListBoxBR.Items 并查看是否找到项目 DisplayMember 和 assignedStudent.FullName 之间的匹配项。

或者您可以在 indexOf 调用中使用 Student 对象，但是您需要确保实现 IEquatable、覆盖 Equals、GetHashCode 等。

Answer 2

您的 checkedListBoxBR 的项目是 Student 类型，因为您的 DataSource 中的项目是 Student:

类型

List<Student> BRStudents = [...]
checkedListBoxBR.DataSource = BRStudents;

通过使用带有字符串 (Student.FullName) 作为参数的 IndexOf 函数，您可以将多个 Student 对象与一个字符串进行比较。没有 Student 等于您的字符串，因此您得到 -1 的结果。尝试像这样修改您的代码：

int assignedStudentIndex = checkedListBoxBR.Items.IndexOf(assignedStudent);

此外，您可能想要 override the Equals method。

编辑：正如@olivier-de-meulder 正确指出的那样，您需要将这些行移到查找上方才能使任何选项起作用：

checkedListBoxBR.DataSource = BRStudents;
checkedListBoxBR.DisplayMember = "FullName";
checkedListBoxBR.ValueMember = "StudentID";

为什么通过 IndexOf() 找不到 CheckedListBox 中存在的项目？

Why is the item that exists in the CheckedListBox not found via IndexOf()?

c#

indexof

checkedlistbox

listboxitems

更新

更新 2

更新 3